1. Field of the Invention
The present invention relates to a color cathode ray tube, and more particularly, to a color cathode ray tube capable of obtaining a structural intensity of a mask corresponding to a panel, decreasing a partial doming, and increasing a drop characteristic by setting a curvature of the panel to be greater from a center portion of the panel towards a peripheral portion thereof.
2. Description of the Related Art
Generally, a color cathode ray tube is for implementing images, and is divided into a curved type cathode ray tube and a flat type cathode ray tube according to an appearance of a panel.
The curved type cathode ray tube has several problems such as an image distortion, eyes fatigue due to light reflection, and etc. thus to have decreasing demands, whereas the flat type cathode ray tube has advantages in that images are not distorted, reflection for external light is minimized, and maximization of a visual region can be implemented thus to have increasing demands.
FIG. 1 is a longitudinal section view showing a color cathode ray tube in accordance with the conventional art.
As shown, the conventional color cathode ray tube comprises a panel 1 having a fluorescent surface 1a, a mask 2 for selecting colors of electron beams incident from an inner side of the panel 1, a funnel 3 coupled to a rear surface of the panel 1 for maintaining inside of the cathode ray tube as a vacuum state, an electron gun 5 mounted in a neck portion 4 of the funnel 3 for emitting electron beams, and a deflection yoke 6 for surrounding outside of the funnel 3 and deflecting electron beams.
In the conventional color cathode ray tube, when image signals are inputted to the electron gun 5, the electron gun 5 emits electron beams and the emitted electron beams are accelerated and focused towards the panel 1 according to voltages applied from each electrode of the electron gun 5.
At this time, the electron beams are deflected by the deflection yoke 6 thus to pass slots formed at the mask 2, and thereby colors of the electron beams are selected. Then, the electron beams collide with the fluorescent surface 1a inside the panel 1 thus to make each fluorescent surface 1a emit light, thereby reproducing images.
In the conventional color cathode ray tube, a method for reducing a center thickness of a panel or a method for flattening an inner surface of a panel were used in order to make the cathode ray tube light and to reduce a cost.
However, in the method for reducing a center thickness of a panel, when the center thickness of a panel becomes thinner than a current standard of 10.5 mm, x-ray emission amount is increased thus to have a limitation.
Also, in the method for flattening an inner surface of a panel, the inner surface of a panel becomes gradually flat and thereby a curvature of a mask becomes gradually flat, thereby decreasing a structural intensity of a mask and thus deteriorating a drop quality (a drop characteristic). Also, when the panel mask becomes flat, electron beams which have passed through mask holes do not correctly hit red, green, and blue phosphors of a screen by a thermal expansion of the mask, thereby generating a partial doming that a color purity of a screen is deteriorated.
To prevent said partial doming, in the conventional art, invar steel, a low thermal expansion material instead of AK, a high thermal expansion material was used to fabricate a mask, which was disclosed in Japanese patent 1984-15861.
In case of using a mask of said invar steel material (hereinafter, invar mask), a thermal expansion of a mask can be decreased. However, in this case, the cost is high, a mechanical workability is very poor thus to have an annealing process temperature more than 900° C., and a metallic pattern has to be heated at the time of forming the mask.
Also, the invar mask has a low structural intensity compared to a mask of AK material (AK mask) and causes a drop characteristic deterioration, so that a wedge ratio of a panel (a ratio of a corner thickness of a panel for a center thickness) was set to be 220% or more than and a mask curvature was set to be similar to a spherical type, that is, to be similar to a single curvature radius R in the conventional art. According to this, an optimum curvature of a panel which is light, reduces a fabrication cost, and increases a structural intensity could not be implemented.